Machine-to-machine (M2M) communication (also referred to as machine type communication (MTC)) establishes communication between machines and between machines and humans. The communication may include exchange of data such as signaling, measurement data, configuration information, etc. The device size may vary from that of a wallet to that of a base station. M2M devices are often used for applications like sensing environmental conditions (e.g., temperature reading, etc.), metering or measurement (e.g., electricity usage, etc.), fault finding or error detection, etc. In these applications the M2M devices may be inactive for relatively long periods of time. For example, depending on the type of service, the M2M device may be active for about 200 ms every 2 seconds, about 500 ms every 60 minutes, etc. The M2M device may also perform measurements on other frequencies or other radio access technologies (RATs).
A particular category of M2M devices may be referred to as low cost devices. Cost reduction may be realized by relaxing the requirements on peak rate and receiver performance. Long term evolution (LTE) Release 12 introduces a low cost user equipment (UE) category referred to as UE category 0. It specifics a relatively low peak rate of 1 Mbps and relaxed performance requirements that can be satisfied by a UE with a single antenna receiver. Cost is further reduced by supporting only half duplex (HD) capability instead of full duplex (FD) capability. Because the UE does not transmit and receive at the same time, the UE does not need a duplex filter. Additional cost reduction techniques include reducing UE bandwidth to 1.4 MHz.
Another category of M2M devices facilitate enhanced uplink (UL) and/or downlink (DL) coverage. These devices are installed at locations where path loss between the M2M device and the base station can be very large, such as a sensor or metering device located in a remote location like a building basement. In such locations, receiving a signal from a base station can be challenging. For example, the path loss can be 15-20 dB worse than what is considered normal operation. To cope with such challenges, the coverage in uplink and/or in downlink is substantially enhanced. Enhanced coverage is achieved by various techniques in the UE and/or in the network node (e.g., boosting DL transmit power, boosting UL transmit power, enhanced UE receiver, signal repetition, etc.).
MTC UEs operating with reduced bandwidth (e.g., 1.4 MHz) may be referred to as narrowband MTC operation, a narrowband MTC, or simply narrowband operation. A narrowband MTC may be scheduled with only six physical resource blocks (PRBs). An allocation of a single PRB for uplink or a single PRB for downlink is possible. Additionally, retuning the frequency of a MTC UE facilitates frequency multiplexing of users and frequency hopping.
For existing LTE UE categories, filtering requirements are defined based on the transmit-to-receive (TX-RX) frequency separation for a given frequency band as defined in TS 36.101 Table 5.7.4 as well as the defined radio frequency (RF) performance requirements of a given LTE UE category. For example, the transmit-receive carrier center frequency separation can be 190 MHz for E-UTRA band 1 (i.e., 2 GHz) and 45 MHz for band 8 (i.e., 900 MHz).
FIG. 1 illustrates an example transmit-receive frequency separation for frequency division duplex (FDD) operation. FIG. 1 illustrates an uplink band and a downlink band separated by a band gap. A subset of PRBs in the uplink band is allocated for narrowband uplink operation and a subset of PRBs in the downlink band is allocated for narrowband downlink operation. The separation between the center of the subset of PRBs in the uplink band and the center of the subset of PRBs in the downlink band is referred to as the duplex spacing.
Using a narrower transmit-receive frequency separation may result in self-interference between the MTC UE transmitter and receiver that exceeds the filtering ability of the MTC UE and prevents the MTC UE from meeting its expected performance levels. This may degrade the error rate performance of the MTC UE and/or reduce the coverage capabilities of the MTC UE. Such a situation can occur if the uplink and downlink PRB allocations for full duplex FDD transmissions are assigned independently. For example, FIG. 1 illustrates assigned uplink PRBs that are close to the upper edge of the uplink band and assigned downlink resources that are close to the lower edge of the downlink band. In this scenario, if the band gap is significantly smaller than the permitted minimum transmit-receive carrier frequency separation, the UE's duplexer filtering may not be sufficient to meet its expected performance requirements.
Resource blocks may be allocated in any part of the spectrum in the downlink or uplink parts of the hand. In other words, the narrow bandwidth operations (e.g., six RBs or less) may be supported in both RF and baseband anywhere in frequency within the cell system bandwidth, such as illustrated in FIG. 2.
FIG. 2 illustrates an example transmit-receive frequency separation for narrowband operation. FIG. 2 illustrates an uplink band and a downlink band separated by a band gap. Also identified are the UL carrier center frequency and the downlink carrier center frequency. A subset of six PRBs in the uplink band is allocated for narrowband uplink operation and a subset of six PRBs in the downlink band is allocated for narrowband downlink operation. As illustrated, the transmit-receive frequency separation of the uplink and downlink bands is larger than the transmit-receive frequency separation of the narrowband uplink and downlink allocation. The transmit-receive frequency separation of the narrowband uplink and downlink allocation is not much greater than the band gap.
Based on the requirements described above for low cost narrowband MTC UEs, the minimum transmit-receive frequency separation can be less than the specified value for each band. Furthermore, the MTC UE may transmit with full power in a narrow bandwidth close the band edge. Accordingly, ensuring that the duplexer gap is sufficient to support existing performance requirements may include defining a minimum separation between transmit and receive carriers within the frequency band for narrowband MTC operation. If the performance requirements cannot be met by the transmit-receive separation, then an alternative is to reduce transmit power to compensate accordingly.
A UE typically performs radio measurements on the serving (as well as on neighbor cells) over some known reference symbols or pilot sequences. The UE may perform measurements on an intra-frequency carrier, inter-frequency carrier(s) as well as on inter-RAT carriers(s) (depending upon the UE capabilities). To enable inter-frequency and inter-RAT measurements, the network may configure measurement gaps.
The measurements serve various purposes. Example measurement purposes include: mobility, positioning, self-organizing network (SON), minimization of drive tests (MDT), operation and maintenance (O&M), network planning and optimization, etc. Examples of UE measurements in LTE include cell identification (i.e., physical cell ID (PCI) acquisition), system information (SI) acquisition, reference symbol received power (RSRP), reference symbol received quality (RSRQ), CSI-RSRP, CSI-RSRQ, discovery signal measurements, cell global identity (CGI) acquisition using autonomous gaps, reference signal time difference (RSTD), UE Rx-Tx time difference measurement, radio link monitoring (RLM), which consists of out of synchronization (out of sync) detection and in synchronization (in-sync) detection, etc.
The UE typically obtains radio measurements by averaging more than one sample or snapshot in the time and/or frequency domain. For example, a UE may perform RSRP/RSRQ measurements over 200 ms by averaging 4 or 5 snapshots or samples taken every 40 or 50 ms where each snapshot may be 1 or 2 ms long.
A UE performs channel state information (CSI) measurements that the network uses for scheduling, link adaptation, etc. Examples of CSI measurements or CSI reports include channel quality indication (CQI), pre-coding matrix indicator (PMI), rank indicator (RI), etc. The UE may perform CSI measurements on reference signals like cell specific reference signals (CRS), CSI reference signals (CSI-RS), or demodulation reference signals (DMRS).
To support functions such as mobility (e.g., cell selection, handover, etc.), positioning, link adaption, scheduling, load balancing, admission control, interference management, interference mitigation, etc., the network node also performs radio measurements on signals transmitted and/or received by the network node. Examples of such measurements include signal-to-noise ratio (SNR), signal-to-interference-plus-noise ratio (SINR), received interference power (RIP), block error ratio (BLER), propagation delay between UE and the network node, transmit carrier power, transmit power of specific signals (e.g., Tx power of reference signals), and positioning measurements like time advance (TA), eNodeB Rx-Tx time difference, etc.
In LTE a UE performs radio measurements on radio signals (e.g., discovery signals, reference signals, etc.) that are transmitted in predefined time-frequency resources. For example, the UE performs cell identification using PSS/SSS, which are transmitted in the central six resource blocks of the downlink carrier frequency in a cell (i.e., in the six central RBs of cell transmission bandwidth). Similarly, a UE measures RSRP and RSRQ on the six central RBs of the bandwidth of an identified cell.
The MTC UE may, however, be configured to operate in a narrow bandwidth. Narrow bandwidth operation is characterized by a UE operable to use fewer resource blocks compared to a total number of RBs in system bandwidth. This is referred to as a narrower bandwidth with respect to system bandwidth. In narrow bandwidth operation, the RF filter in the UE for uplink and/or downlink operation is tuned over the narrower RF bandwidth. In traditional LTE operation, particular data or control channels may be transmitted over a subset of RBs, but the RF bandwidth is the same as that of the system bandwidth. An example of narrow bandwidth (or narrower RF bandwidth) is an RF bandwidth of 1.4 MHz containing six RBs in a system bandwidth of 10 MHz containing fifty RBs. Narrow bandwidth operation is also characterized by a narrower transmit-receive carrier center frequency separation (δf) within the system bandwidth. For example, the narrow band may comprise a transmit-receive frequency separation of 27 MHz compared to a pre-defined or default value (ΔF) such as 35 MHz for the system bandwidth.
These two attributes of narrow bandwidth operation may prevent a UE from receiving the necessary radio signals required for performing one or more radio measurements. Furthermore, because of narrow transmit-receive carrier center frequency separation (δf), UE uplink transmissions may cause self-interference with the UE's own receiver. These factors may degrade mobility performance of the MTC UE and may even result in call dropping, handover failure, positioning failure, etc.